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Its high-relief topology, active seismic zone, and intense summer monsoons make Nepal very prone to the occurrence of multiple hazards, among which droughts and landslides (MoHa, 2019). The impact of droughts on the food security and economic development in Nepal is considerable since 65% of the households relies on rain-fed farming (FAO, 2020). Also, landslides have a large impact on the liveability in Nepal, causing considerable economic losses and fatalities every year (Petley et al., 2007); in 2017 and 2018 a total of 484 landslides were reported in Nepal, leading to 161 casualties and an economic damage of 1.6 million USD (MoHa, 2019). To improve drought and landslide risk awareness and preparedness, real-time monitoring of these hazards is necessary. Although many systems monitoring these hazards have been developed and implemented, these systems or their applications often only provide hydrometeorological information displayed on low spatial resolution. There is, however, a need for information that is comprehensible, directly applicable, and, therefore, helpful to drought and landslide risk awareness and early warning on local scale. Therefore, this study has investigated methodologies and visual output for a multi-hazard monitoring model that provides accessible information on agricultural drought occurrence and rainfall-triggered landslide potential in the Trishuli river basin of Central Nepal. These methodologies use meteorological variables at point scale obtained from ECMWF’s ERA5 product that is downscaled with meteorological station measurements at different locations throughout the catchment area. For the monitoring of drought impact on rice, wheat, and maize production a visualisation is developed, indicating crop seasonal water availability based on the estimation of Makkink evapotranspiration and a subsequent climatic water balance. Landslide risk has been estimated by comparing the daily index of antecedent rainfall (ARI) to a threshold of extrem

We present changes of the ice margin in Northwest Greenland at the Eastern part of the Nunatarssuaq Ice Cap (NIC) over six decades. The ice margin in this area terminates as a near-vertical ice cliff of between 9 and 33 m thickness. During the years 1954–1957 and in 1965 multi-disciplinary studies were performed. We digitise and orthorectify material, that is often difficult to access, in order to use the historical data as an absolute starting point of our change assessment. We compare the cliff morphology of the mid-1950s and the mid-1960s with various time-steps between 1985 and 2017. The studied ice margin remained remarkably constant with very subtle changes of changing sign: rather slow advance rates are reported from the 1950s and 1960s that accelerated until 1985 and were followed by a general retreat until 2012 and a subsequent advance until 2017. Thickness changes are negative throughout the entire time-period, however, different rates of thinning are shown and there is a positive relationship with air temperature anomalies. Compared to similar elevations on the adjacent Greenland ice sheet, we find significantly weaker thinning rates at the NIC.

Melting snow and glacier ice in the Himalaya forms an important source of water for people downstream. Incoming longwave radiation (LWin) is an important energy source for melt, but there are only few measurements of LWin at high elevation. For the modelling of snow and glacier melt, the LWin is therefore often represented by parameterizations that were originally developed for lower elevation environments. With LWin measurements at eight stations in three catchments in the Himalaya, with elevations between 3,980 and 6,352 m.a.s.l., we test existing LWin parameterizations. We find that these parameterizations generally underestimate the LWin, especially in wet (monsoon) conditions, where clouds are abundant and locally formed. We present a new parameterization based only on near‐surface temperature and relative humidity, both of which are easy and inexpensive to measure accurately. The new parameterization performs better than the parameterizations available in literature, in some cases halving the root‐mean‐squared error. The new parameterization is especially improving existing parameterizations in cloudy conditions. We also show that the choice of longwave parameterization strongly affects melt calculations of snow and ice.

Schuttbedeckte Gletscher kommen in praktisch allen vergletscherten Gebirgen der Erde vor. Der Schutt wird von verschiedenen Herkunftsorten um, über und unter dem Gletscher auf die Gletscherzunge transportiert – zahlreiche Prozesse greifen dafür ineinander. Einmal dort abgelagert beeinflusst der Schutt die Schmelzrate des darunterliegenden Gletschereises wesentlich. Eine wichtige Funktion fällt dabei der Mächtigkeit und der Zusammensetzung des Schuttmantels zu, welche bestimmen, ob das darunterliegende Eis gegenüber der schuttfreien Gletscherfläche schneller schmilzt, oder ob das Eis durch die darüberliegende Schuttschicht isoliert und dadurch thermisch geschützt wird. Der Schutt verändert aber auch die Oberflächeneigenschaften dieser Gletscher grundlegend, wobei vor allem kleine Schmelzwasserseen und Eisklippen, aber auch veränderte Fliesseigenschaften einen grossen Einfluss auf die Massenverluste der Gletscherzunge haben können. Wissenschaftler suchen unter anderem nach Fernerkundungsmethoden, die Dicke der Geröllschicht auf den Gletscherzungen flächendeckend besser abzuschätzen. Messungen von schuttbedeckten Gletschern werden sowohl direkt auf deren Oberfläche als auch aus der Luft oder dem All vorgenommen, wobei das Hauptaugenmerk vor allem auf den meteorologischen Bedingungen, den Schutteigenschaften und deren räumlichen und zeitlichen Variabilität liegt. Glacier melt under debris: Distribution, processes and measuring methods: Debris-covered glaciers occur in basically all glacierized mountain ranges on Earth. The debris is transported onto the glacier tongue by a variety of processes, originating from different zones around, above and below the glacier. Once deposited there, the debris significantly affects the melting rate of the underlying ice. An important function here is the thickness and the composition of the debris mantle, which determine whether the underlying ice melts faster compared to the debris-free glacier surface or whether the ice is

Remotely Piloted Aircraft Systems (RPAS) have become an important tool in studying glaciers and their surfaces as they can generate high-resolution ortho-images and digital elevation models (DEM). It is important to monitor the surface of the Greenland Ice Sheet (GrIS) as it has become the largest cryospheric contributor to sea-level rise. Glacier surface energy balance models can provide insight in the mass loss rate and show that turbulent fluxes can form a major component. Aerodynamic roughness is an important parameter in these models, for which currently a fixed value is often used. This paper therefore analyses the possibilities of using RPAS-derived DEMs to quantify topographic roughness and its impact on turbulent energy fluxes on the GrIS. To answer this question, the following two unique methods were developed. First, the Moving Footprint (MF) method which produces a roughness estimate for a single location by moving a rotating footprint of varying size over the DEM. This footprint then extracts transects to which commonly used microtopographic algorithms (Lettau, Munro, and Nield) were applied. Second, the Fixed Grid (FG) method which produces a distribution of roughness values over the study area, by subdividing the study area in grid cells in which commonly used microtopographic algorithms (Lettau, Munro, and Nield) were applied. Our results show that both methods can produce realistic roughness estimates for a range of scales using certain algorithms. In the MF method, the Lettau algorithm performs well, while in the FG method, the Munro, Nield SdElev and Nield Max algorithms perform well. Moreover, we prove that the simulated sensible heat fluxes using roughness values derived using the MF method (Lettau, 5x40m footprint) or FG method (Munro, Nield SdElev, 5m grid size) are as accurate as simulated sensible heat fluxes using roughness values obtained by aerodynamic inversion of automatic weather station (AWS) data. The implication of these findings ar

Ice cliffs and ponds on debris-covered glaciers have received increased attention due to their role in amplifying local melt. However, very few studies have looked at these features on the catchment scale to determine their patterns and changes in space and time. We have compiled a detailed inventory of cliffs and ponds in the Langtang catchment, central Himalaya, from six high-resolution satellite orthoimages and DEMs between 2006 and 2015, and a historic orthophoto from 1974. Cliffs cover between 1.4% (± 0.4%) in the dry and 3.4% (± 0.9%) in the wet seasons and ponds between 0.6% (± 0.1%) and 1.6% (± 0.3%) of the total debris-covered tongues. We find large variations between seasons, as cliffs and ponds tend to grow in the wetter monsoon period, but there is no obvious trend in total area over the study period. The inventory further shows that cliffs are predominately north-facing irrespective of the glacier flow direction. Both cliffs and ponds appear in higher densities several hundred metres from the terminus in areas where tributaries reach the main glacier tongue. On the largest glacier in the catchment ~10% of all cliffs and ponds persisted over nearly a decade.

Debris-covered glaciers in the Himalaya play an important role in the high-altitude water cycle. The thickness of the debris layer is a key control of the melt rate of those glaciers, yet little is known about the relative importance of the three potential sources of debris supply: the rockwalls, the glacier bed and the lateral moraines. In this study, we hypothesize that mass movement from the lateral moraines is a significant debris supply to debris-covered glaciers, in particular when the glacier is disconnected from the rockwall due to downwasting. To test this hypothesis, eight high-resolution and accurate digital elevation models from the lateral moraines of the debris-covered Lirung Glacier in Nepal are used. These are created using structure from motion (SfM), based on images captured using an unmanned aerial vehicle between May 2013 and April 2018. The analysis shows that mass transport results in an elevation change on the lateral moraines with an average rate of −0.31±0.26 m year−1 during this period, partly related to sub-moraine ice melt. There is a higher elevation change rate observed in the monsoon (−0.39±0.74 m year−1) than in the dry season (−0.23±0.68 m year−1). The lower debris aprons of the lateral moraines decrease in elevation at a faster rate during both seasons, probably due to the melt of ice below. The surface lowering rates of the upper gullied moraine, with no ice core below, translate into an annual increase in debris thickness of 0.08 m year−1 along a narrow margin of the glacier surface, with an observed absolute thickness of approximately 1 m, reducing melt rates of underlying glacier ice. Further research should focus on how large this negative feedback is in controlling melt and how debris is redistributed on the glacier surface.

This study aims at developing and applying a spatially-distributed coupled glacier mass balance and ice-flow model to attribute the response of glaciers to natural and anthropogenic climate change. We focus on two glaciers with contrasting surface characteristics: a debris-covered glacier (Langtang Glacier in Nepal) and a clean-ice glacier (Hintereisferner in Austria). The model is applied from the end of the Little Ice Age (1850) to the present-day (2016) and is forced with four bias-corrected General Circulation Models (GCMs) from the historical experiment of the CMIP5 archive. The selected GCMs represent region-specific warm-dry, warm-wet, cold-dry, and cold-wet climate conditions. To isolate the effects of anthropogenic climate change on glacier mass balance and flow runs from these GCMs with and without further anthropogenic forcing after 1970 until 2016 are selected. The outcomes indicate that both glaciers experience the largest reduction in area and volume under warm climate conditions, whereas area and volume reductions are smaller under cold climate conditions. Simultaneously with changes in glacier area and volume, surface velocities generally decrease over time. Without further anthropogenic forcing the results reveal a 3% (9%) smaller decline in glacier area (volume) for the debris-covered glacier and a 18% (39%) smaller decline in glacier area (volume) for the clean-ice glacier. The difference in the magnitude between the two glaciers can mainly be attributed to differences in the response time of the glaciers, where the clean-ice glacier shows a much faster response to climate change. We conclude that the response of the two glaciers can mainly be attributed to anthropogenic climate change and that the impact is larger on the clean-ice glacier. The outcomes show that the model performs well under different climate conditions and that the developed approach can be used for regional-scale glacio-hydrological modeling.

We use high-resolution digital elevation models (DEMs) from unmanned aerial vehicle (UAV) surveys to document the evolution of four ice cliffs on the debris-covered tongue of Lirung Glacier, Nepal, over one ablation season. Observations show that out of four cliffs, three different patterns of evolution emerge: (i) reclining cliffs that flatten during the ablation season; (ii) stable cliffs that maintain a self-similar geometry; and (iii) growing cliffs, expanding laterally. We use the insights from this unique data set to develop a 3-D model of cliff backwasting and evolution that is validated against observations and an independent data set of volume losses. The model includes ablation at the cliff surface driven by energy exchange with the atmosphere, reburial of cliff cells by surrounding debris, and the effect of adjacent ponds. The cliff geometry is updated monthly to account for the modifications induced by each of those processes. Model results indicate that a major factor affecting the survival of steep cliffs is the coupling with ponded water at its base, which prevents progressive flattening and possible disappearance of a cliff. The radial growth observed at one cliff is explained by higher receipts of longwave and shortwave radiation, calculated taking into account atmospheric fluxes, shading, and the emission of longwave radiation from debris surfaces. The model is a clear step forward compared to existing static approaches that calculate atmospheric melt over an invariant cliff geometry and can be used for long-term simulations of cliff evolution and to test existing hypotheses about cliffs' survival.

Mass losses originating from supraglacial ice cliffs at the lower tongues of debris-covered glaciers are a potentially large component of the mass balance, but have rarely been quantified. In this study, we develop a method to estimate ice cliff volume losses based on high-resolution topographic data derived from terrestrial and aerial photogrammetry. We apply our method to six cliffs monitored in May and October 2013 and 2014 using four different topographic datasets collected over the debris-covered Lirung Glacier of the Nepalese Himalayas. During the monsoon, the cliff mean backwasting rate was relatively consistent in 2013 (3.8 ± 0.3 cm w.e. d−1) and more heterogeneous among cliffs in 2014 (3.1 ± 0.7 cm w.e. d−1), and the geometric variations between cliffs are larger. Their mean backwasting rate is significantly lower in winter (October 2013–May 2014), at 1.0 ± 0.3 cm w.e. d−1. These results are consistent with estimates of cliff ablation from an energy-balance model developed in a previous study. The ice cliffs lose mass at rates six times higher than estimates of glacier-wide melt under debris, which seems to confirm that ice cliffs provide a large contribution to total glacier melt.